Induction-coil.



c. A. FERR ELL.

INDUCHON COIL. APPLICAHON FILED OCT. M 1915.

Patented Apr. "24, 1917.

J 5. M M M? MW w CHARLES A. FERRELL, (2F GLEVEL no, onto, on caravans Application filed Qctcber 3.915. Serial No. 541,6 5.

To all whom it concern Be it known that I, Cnnnnns A. Farms-Ln, Y

a citizen of the United States, residing at Cleveland,'in the county of Cuyahoga and State of Ohio, have invented a certain new and useful Improvement in Induction-Coils, of which the following is a full, clear, and exact description, reference being had to the accompanying drawings This invention relates to induction coils and particularly to coils of a jump spark nature such as are used in the igni on internal combustion engines. the transmission of wireless telegraph signals, the

operation of high frequency apparatusgalso in connection with certain types of transformers and in certain operations or 'ohysics and chemistry. In such dejlces is well known, an interrupted or alternating current on a primary of few turns is stepped up into an alternating current greatly increased voltage by means'of a secondary 'coil of many turns. Diiliculty has sometimes been experlenced from a burning out SEC- or short circuiting o1 piercing of the ondary'coll and it is the ObjQCl of the present invention to overcome this condition in a simple and scientific manner, without inipairing the operation of the coil.

For the production of an eilicient induction coil it is necessary to concentrate the wire of the secondary winding into a small compass so as to include practically all or at least the greater part of it it idc the maximum field of the prin'iary winding and magnetized core.

This necessarily sets a limit upon the amount of insulation which can be used between adjacent layers and between adjacent turns in the same layer. However, a secondcondition which is to be met is the fact that if an insulation of high specific inductive capacity be employed, the result is such increase of the condenser effect between successive layers (and even between successive turns in the same layer) as markedly to change the chzvacter of the spark, reducing a spark which would otherwise be fat and hot into one which is lean ing; in the body of the coil can be carried;

also the specific inductive capacity of the" dh-dectric influences the condenser effect, since ,;-")G1il1'l1'lt shows that a dielectric like niica or muslinsutureted-with-linseed-oil if used oughout the coil will produce a spark w a coil in which dry paper or some similar substance-of low dielectric strength is used between successive layers, and air (or some flocculent like silk} is used between the adjacent turns will ailord a spark which is noiseless and extren'iely hot; the same number of tur and the some general'diinensinus of coil being employed between the two In fact the nature of the insulation op n the wire itself is important in enameled wire beiiig ineffective a hot spark because of the high specific inductive capacity-of the insulation, but silk and cotton being fully satisfactory because of the smaller condenser action.

in a coilwound as above described, the factor of safety of the insulation is obviously none too high betweenadjacent turns or between adjacent layers, although experience shows that breakdown, burning,. or puncturing of the insulation is confined to a point either at or closely adjacent to the free terminals of the secondary Winding. in case both ends of the secondary winding are brought out in the form of free terminals, the observed :t'ailureof the insulation may occur at either end; if one end of the secondary be grounded upon the primary, as is frequently done in high frequency work and engine ignition, there apiears to he only one place where failure of insulation heed be anticipated, namely at the free terminal of the secondary coil or withii'i a few tnrns'thcretroin. ther discovered that during the, operation of coil of this nature there isi superimposed upon the ordinary and generally described secondary action a static surging. eiiect wherein the amount of electricity involved I have furvolts. This eil'ect, being in the nature of a wave motion, exhibits loops or points of high intensity and nodes or points of low intensity, and such a loop always occurs at or near the free terminal of the secondmy coil. Under favorable conditions the effect of this small high potent1a1.stat1c charge appears to be to form a path through the insulation and ionize the air along such path after which the true secondary discharge of larger quantity but lower poten-' tial is enabled to pass with its well known heating and disintegrating effect.

In order to overcome this danger of break down, or puncturing, I increase the insulation of the last layer or of the last few turns adjacent toteach free turn on the secondary coil. In case the inner end of the seconda coil is grounded upon the primary as 1susually the case in high frequenc coils and in engine ignition, this'increase o insulation is necessary only upon the outer layer. It is entirely a matter of convenience whether the excessive insulation be applied to the entire final layer or only to the few turns at the extreme end thereof, although the former construction is generally adopted as a matterof convenience. This additional insulation may either be a matter of uantity or of quality. Thus I may achieve t e same by winding the last few turns in a more open manner than the remainder of the'coil and over and around a larger amount of insulation of the same kind, different kind oflinsulation, such as mica or cloth saturated with linseed oil, since the condenser action consequent upon the higher dielectric strength through this small region is found not to impede the production of a hot discharge.

In the drawings accompanying and forming a part of this application wherein I have illustrated certain embodiments of my invention, Figure l is a partly diagrammatic and partly sectional view of an induction coil showing my improvements applied thereto; Fig. 2 is a similar view of a different type of secondary winding constructed in accordance with my invention; Fig. 3 is a view similar to Fig. 2 showing a modified form of secondary winding; Fig. 4 illustrates that form of my invention wherein I employ insulating materials of varying specific inductive capacities: Fig. 5 illustrates a double ended coil constructed in accordance with one form of my invention; and

Fig. 6 illustrates a variety of pancake 'wind 111;: having my improvements applied I thereto.

Describing the parts by reference characters, first taking up Fig. l, 1 represents conventionally the core of an induction coil proeffect.

or I may employ a as illustrated at 16,

. closely together and vided with a primary winding 2 connected through an interrupter 3 with a battery or like source 4, a condenser 5 being connected around the interrupter, 6 represents the secondar coil which is wound in the form of a cylin rioal spool containing a pluralit'y of layers of fine wire as shown at 7, successive layers being insulated from each other by thin paper or like material. Preferably this paper is not impre nated with any wax, gum or the like since t e effect of such impregnation would greatly increase the dielectric strength and therefore the condenser In Fig. 1 I have shown one of the terminals at 8 as grounded upon the primary and the other at 9 as led freely awa from the secondary as customary in high frequency and engine ignition practice. In this view I have shown the outermost layer 10 as separated from the layer beneath by an unusually large amount of insulation 11, and have shown the half dozen turns nearest the end spaced comparatively widely apart as shown at 12. In this embodiment the insulation at llis supposed to be of the same nature as that 'of the rest of the coil and similarly unimpregnated, although impregnated material may be used at this point within the scope of my invention; the requirement being an excess of some nature at this point.

In Fig. 2 I have shown a secondary coil removedfro'm the primary and having both of itsterminals free for separate connection. In this embodiment the initial turns of the first layer of the secondary coil are s aced widely apart and a comparatively large amount of insulation as shownat 15, and the-final turns of the outside layer of the secondary coil are similarly spaced apart and abundantly insulated the remaining turns of layers as well as of all being crowded more separated by a much smaller amount of insulation as shown at 17. In eaclrof the embodiments shown in Figs. 1 and 2 the insulation between adjacent layers is uniform, from one end of the coil to the other, the layers which carry the ter minals being uniformly spaced away from the adjacent layers by the excess insulation. In Fig. 3 I have illustrated a third form of secondary coil in which one of the terminals 20 is arranged for connection to the primary winding while the other terminal 21 communicates with a few turns of wire 22 the initial and'final intermediate layers surrounded on all-si es by which are spaced more widely apart than esser? iii- 1 actually made and used successfully, but the construction which I now prefer is that illustrated in Fig. dwherein represents a cylindrical spool having an end 26 of suit- -able insulating materiril. Wire is wound thereon in layers asshown at 2?, the wire being preferably cotton-covered, the adjacent turns of each layer being; insulated chiefly by air. Adjacent layers are separated by unimpregnated paper and prefer ably very thin paper wound in several layers so as to obtain the benefit of the included air spaces. The whole coil is built in this manner until the final layer is reached whereupon an insulating layer 28 of higher insulating strength is employed, such as mica, oiled silk, or thelike. Also the final turns adjacent the terminal 29 are preterably spaced apart somewhat more widely than the turns in the body'of the coil. So far as the prevention of puncturing is concerned it is suiiicient to confine this increased insulation to a short distance at the end or". the layer, but for purposes of manufacturing convenience I enerally make the whole layer uniform an this does not seriously impair the quality of the discharge.

In Fig.=-'5 l have shown a double ended coil wherein both termini of the secondary are led out. Each of the coils is preferably wound in the manner shown in Fig. 4:; the inner ends being coniiected at 30. Sf course, the direction of winding of'the two coils must be so chosen thattheir inductive eficc'ts may be added together, and when so constructed the points 30 cause a node and not successively with insulated wire spun therein without any attempt at insulation excepting the cotton or silk coverings. in this case my invention is-performed by including inside the outer layer of each terminal groove a thickness of mice or oiled silk as shown at 34, and preferably spacing the turns outside ofthis insulation slightly more widely.

While the same eflect of obtaining freedom from breakdown could be obtained by winding all of the turns of-the whole coil similarly spaced apart'imd similarly carefully insulated, such a construction would defeat the very purpose of the coil which is to produce ei'hot, high-potential, efiicient spark; since the comparatively great up which the coil would necessarily ocean order to permit such unifm-m cries" sulation would greatly increase tho sistanee or copper loss and would the outside turns of the coil so for 1 influence of the magnetic field no primary as greatly to decrease its Also, as already explained this do? e breakdown would be overcome by mica, oil silk, or the like for the insu in the body of the coil as well zit-the minal layers, but this would impair the action of the coil by reason of the reater specific inductive capacity of the dielectric. By my invention, I avoid all condenser eii by employing an insulation-of minimum electric strength, I retain a cone-entraied action by using the smallest practicable quantity of insulation, and finally achieve freedom from breakdown by reinforcing; the weakest points, either by greater tity or higher quality of insulation. might be argued that a similar avoiding oi puncturing would be attained by discovering' one of the nodal points above mentioned and cutting back the terminal to thutpoint.

However this will be found to rearrange whole wave motion, shifting the nodal points so that the terminal connection would still remain at a. loop."

It will also be understood that the inveution is equally applicable to high tension magneto windings and to' ill coils connected with pulsating or intermittent currents.

While I have described m invention at length and set forth the theoryof operation so for as l have been able to discover t e same, still do not confine rnyse it to theories herein set forth but only methods, constructions, and con whereby the results at end not specifically o e" v same are defini'mly recited Y hereto annexed or rendered necw prior state of the 1 Having thus descrihed my invention, I claim isz- 1. An induction coii secondary iav 1 difi'erent layers of wire within its arated by insulating material of lo inductive capacity and having "the jacent each free terminal separated from the remainder of the. coil by insulating 'of higher specific inductive capacity. T 2. An induction coil secondery ilZW'l'L adjacent layers of wire in its body portion separated by non-impregnated paper and having a. portion adjacent to the free terminals insulated by a layer of suhswntielly the same thickness as theesid layer and of a material'ofhigher s lo iiic induc *tive cupacitylthsn that of paper hereby the'outer ram-r are more effectively cl than the inner turns but are cemphcted t0- .in 'ner turns but are compacted together to 10 I gather to the same extent. the same extent.

3. A coil for electrical use comprising a In testimony whereof, I hereunto alfit my plurality of layers of helically Wound w re, signature in the presence of two witnesses.

the layers in the body of: the coil being separated by thin sheets of dry paper and the CHAflLES BERRELL' terminal layers being insulated by sheets of Witnesses: impregnated material whereby the outer HUGH B. MCGILL, l

turns are more effectively insulated than the ROBERT L. BRUCE- 

